The present invention deals with siloxane compositions which are converted to elastomeric or resinous films upon curing and are further converted to strong, hard ceramic substances when exposed to high temperatures in excess of 500.degree. C.
Silicone resins have been used in a wide variety of fields as electric insulating materials because of their excellent physical properties and electrical properties. For example, electric wires and cables covered with silicone rubber or silicone resins in order to improve the physical strength and electrical insulation are widely known.
These wire or cable coverings of silicone rubber or silicone resins, unlike the inorganic insulating materials, burn away when they are exposed to high temperatures above 500.degree. C. which usually results in a striking decrease or complete loss of electrical insulating performance. Silicone rubber or silicone resins are known to leave inorganic ash as a combustion residue. When these materials are used as electrical insulation, the residual ash either scatters off, or, if it remains on the conducting material, it is extremely brittle, has dehydration cracks and is in such a state that the residual material comes off the conducting material and therefore fails to function as an electrical insulating material.
It is known that some castable silicone materials form ceramics and do not lose their original shapes when they are exposed to high temperatures. However, these materials, at ordinary temperatures, are generally resinous substances without flexibility and they are not suitable as electrical insulating materials for the parts where flexibility is required.
Ceramic products have been known for their excellent heat resistance and electrical properties. However, their use is limited because of the difficulty in working with them.
In recent years materials which can maintain their original shape and electrical insulating property in spite of exposure to high temperatures, such as material for refractory electrical wire for exposed wiring in an emergency electric source circuit, have been in high demand. Japanese Publication No. 51 {1976}-60240 and Japanese Publication No. 51{1976}-82319 are known to respond to these demands. These materials, which have silica fillers as an indispensable component tend to cause the burning of the surface when the cured substance is exposed to high temperatures or they undergo partial foaming, resulting in difficulty in producing uniform ceramified materials of high dimensional stability.
The present invention offers silicone compositions which have overcome the above-mentioned shortcomings of the already existing materials. When these compositions are cured, they become elastomers or resinous substances within the range of temperatures in which these materials are ordinarily used. Upon exposure to high temperatures, these materials are ceramified to yield homogeneous and dense ceramics with excellent dimensional stability, strength and electrical insulating properties.